Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty

published 2026-09-02 2 mo ago modified 2026-09-08 2 mo ago also EUVD-2026-70211

cvss: 5.9; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 10%
public exploits: 0; none known

Multiple vulnerabilities in the Secure/Multipurpose Internet Mail Extensions (S/MIME) decryption functionality of Cisco Secure Email could allow an unauthenticated, remote attacker to recover plain text from encrypted email messages.

These vulnerabilities are due to insufficient validation of message integrity. An attacker could exploit these vulnerabilities by using a machine-in-the-middle technique to intercept and modify traffic between email gateways. A successful exploit could allow the attacker to obtain plaintext content from the encrypted communication.

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 2 mo ago (2026-09-02)

Exploit prediction

0.20% chance of exploitation in the next 30 days, higher than 10% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	5.9	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected products

Cisco Cisco Secure Email

Classification

Weakness

CWE-345 Insufficient Verification of Data Authenticity

References

sec.cloudapps.cisco.com /security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-smime-disc-dzw4rEdY

Sources

CVE List CVE-2026-20355
NVD CVE-2026-20355

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary